The present disclosure sets out an economical oil lift system which is installed with reduced capital expenditures, and which has the benefit of reduced lifting cost during operations. It is intended to be used on stripper wells. Stripper wells are defined as those producing typically up to about 10 barrels of oil per day. They may produce water with the oil in quantities ranging from perhaps 10 or 15 times the volume as water to a negligible amount. As will be understood, stripper wells of that production volume simply are economically marginal and can be operated only if the capital costs and operational costs are reduced. The present disclosure sets out a method and apparatus for providing that kind of reduced capital and operational cost. The typical method of producing a stripper well is to install a wellhead pump jack, a string of sucker rods and a downhole pump. This requires pumping through a tubing string. To be sure, stripper wells are normally straight and relatively shallow requiring minimal installed equipment. Nevertheless, it is necessary to install the equipment in the well. This costs significantly to purchase and install the capital equipment. The wellhead equipment normally entails a walking beam and electric motor at the surface. That has a well known cost dependent on the size of the walking beam and motor. A well known and easily identified cost is also involved in the tubing and sucker rod string having a cost factor based on well depth. The downhole pump is installed at the lower end of the sucker rod string and has a well known cost.
Operational costs include the electricity required to power the pump, and periodic service of the wells. Servicing of a typical stripper well involves periodic removal of the sucker rod string, the tubing string and the downhole pump connected on that. Without regard to the nature of the service, the removal and reinstallation of these components involves a very significant and substantial economic outlay. This service routine is typically undertaken to clean out the well when there is an excessive accumulation of sand around the pump or paraffin along the tubing. Sometimes, the sucker rods must be pulled to inspect them and to make appropriate replacements or to install bumpers on them. Sometimes, sucker rods will drag, thereby damaging the surface of the rod string, and possibly wearing against the adjacent tubular goods. Service has a cost. Service for the present system is distinctly better. To begin with, the cased well is normally open from the wellhead down to the bottom of the well. The well is open so that the service personnel can work on the well without the delay of having to pull sucker rods and tubing. Service is done through the wellhead without the preliminary step of installing a workover rig to pull a few hundred feet of sucker rods. Indeed, a workover rig is often required to service shallow wells with pump jack and sucker rods. Workover rigs of necessity involve a larger truck which has to be driven the remote location of the wellhead, erected over the wellhead and then operated to pull all the tubular goods in the well. That preliminary step, even where the well is only 600 feet deep, takes two or three skilled personnel and requires at least an hour or two of operation ignoring the difficulties of getting the truck to the site and then onto the highway after the service job has been completed. Suffice it to say, the difficulties of servicing can range from relatively easy to tedious and difficult. These are activities and service charges which are avoided by the present oil lift apparatus.
This disclosure sets out a wellhead system which is installed on a skid adjacent to the wellhead which utilizes no sucker rods. Rather, it employs a drum which spools a lifting cable. The drum, cable spooling apparatus and supportive frame or skid are mounted adjacent to the wellhead. This equipment need not be moved at the time of servicing. Rather, the equipment inserted into the well comprises solely a bailing bucket and a long cable. The wireline is spooled on the drum. The wireline is relatively small and has only sufficient diameter to support the weight which is carried on it (often, it is called a slick line). That diameter or cable gauge is discussed in some detail below. The produced oil (and any water which is found with it) is bailed out of the well by an elongate tubular bailing bucket. The bail is raised with a full load of liquid retrieved from the well. It is raised to the wellhead where the liquid is then removed by a pump. The pump has an elongate stinger which extends into the bail, thereby pumping the retrieved liquid out of the bail and into a gathering system. When the bail is in the up position at the top end of its stroke, it delivers the liquid, leaving the cased well substantially clear. For service work, the bail is simply pulled from the wellhead equipment, laid aside for the moment and easy entry into the well is then obtained. Easy entry reduces the setup time to begin service. If the well is sanded up, it is easy to run a wash line into the well to dislodge and retrieve the accumulated sand, etc. At the completion of the service work, the wash equipment is simply pulled from the well and the bail is reinserted into the well. Removal of equipment from the well and restoration of that equipment is done easily.
A longer bail can be used. This longer bail can have sufficient length so that vacuum lift from liquid from the bail is not possible. With the bale in excessive of about 30 feet, the liquid head becomes so great that vacuum removal is not possible. The present disclosure sets out an improved bail where the liquid is removed from the bail by positive air pressure which displaces the liquid. An appropriate bail and stinger construction are set forth to enable this improved removal.
The present apparatus is summarized as equipment which is located at the surface. That equipment includes an elongate horizontal frame or skid which is either rested on the ground or elevated. The skid supports a cable winding mechanism adjacent to a cable storage drum. A level wind device is typically included. This provides a slick line which is extended from the storage reel or drum through the level winding device and then over a single measuring pulley. The pulley directs the cable downwardly into the well borehole. The equipment also includes certain load sensors which respond to the load on the slick line. The load on the line is measured dynamically so that the cable load alters the motor operation so that the cable is lowered from the surface, dropped into the liquid accumulated at the bottom of the well, filled and then the cable is retrieved with the filled bail on it. The bail, full of retrieved liquid, is pulled to the surface. When the bail arrives at the surface, a switch is triggered to stop further movement. In conjunction with that operation, a stinger is inserted into the bail to a depth to enable retraction by pump of the liquid in the bail.
Summarizing further, this disclosure sets forth an improved stinger and bail construction which cooperate together to enable delivery of a column of oil which is longer than 30 feet; it is sufficiently long that it enables removal by air displacement, not by vaccum lift. A stinger is provided which plugs the bale perfectly, thereby enabling air to be pumped into the bail and force any liquid in the bail from the bail into an oil recovery system.